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Nothing But the Facts About Ganymede, Jupiter's Largest Moon

Ganymede is not only Jupiter's largest moon—it is the largest natural satellite in the Solar System. It is larger even than the planets Pluto and Mercury. Ganymede is believed to have an iron core, and is the only moon known to have its own magnetosphere. Spark your interest? See below for more.

Intriguing Features

Spectrogram of Ganymede's Magnetosphere

Credit: JPL/NASA

1) Unique construction. It is believed Ganymede contains a metal center—liquid iron—encased by rock, which is in turn encrusted in ice. This makes Ganymede the most centrally concentrated solid body known in the Solar System!

2) Bring a compass. Ganymede has the distinction of being the only moon with a magnetosphere of its own, though largely overshadowed by Jupiter's huge magnetic fields. The mechanism or mechanisms behind producing it remain uncertain, but evidence hints at an iron core. This suggests the so-called dynamo mechanism is at least partly responsible for it.

3) An atmosphere containing ozone. Although Ganymede's atmosphere isn't very substantial, its constituents are of great interest. In addition to monatomic and diatomic oxygen, the Hubble Space Telescope has revealed the presence of triatomic oxygen—ozone.

4) Underground ocean? Ganymede might have an ocean layer lying beneath its icy exterior, but if so, it would exist as liquid only due to high pressure. Despite the presence of abundant water and some oxygen, Ganymede is likely incapable of supporting life.

5) An atmosphere, but no ionosphere? Because of Ganymede's magnetosphere, oxygen molecules from its atmosphere should be ionized by electron. So far, however, there has been insufficient evidence to indicate the presence of an ionosphere. More detailed data is required.